The Effect of Spatial Variability and Anisotropy of Soils on Bearing Capacity of Shallow Foundations

Naturally occurred soil deposits inherit heterogeneity and anisotropy in their strength properties. The main purpose of this paper is to model the soil stratum with anisotropy consideration and spatially varying undrained shear strength by using random field theory coupled with finite difference numerical analysis to evaluate their effect on the bearing capacity of the shallow foundations. In the present study, undrained shear strength of soil is considered as a stochastic variable and is assumed to be log-normally distributed and spatially correlated throughout the domain. Two kinds of anisotropy of cohesion are incorporated in the analyses. As the first kind, mechanical anisotropy of cohesion was taken into account by generalizing the conventional isotropic Mohr-Coulomb failure criterion to the anisotropic one, and the second kind is the heterogeneity anisotropy associated with difference in the correlation structure of the cohesion data in the horizontal and vertical directions considered by a special anisotropic correlation function. The results showed the importance of different components of anisotropy and the stochastic variation of shear strength parameters. Mechanical anisotropy and the spatial variability of the cohesion showed that they have significant effects on the bearing capacity of the shallow foundations and their negligence will lead to an under-conservatism.